Search Results (463)

The ecological status of the two nautical mile (2 nm) coastal waters of Bulgaria (BG) and Romania (RO) is evaluated in terms of eutrophication, focusing on various environmental and chemical indicators related to nutrient enrichment and its effects. Applying the Blue2 Modelling Framework (Blue2MF) Black Sea model, we simulate diverse combinations of nitrogen (N) and phosphorus (P) reduction. By integrating atmospheric and marine conditions, hydrology and environmental dynamics, the model provides a comprehensive framework for analysing the impact of external pressures on the marine environment and can be used to set regional sustainability goals. Each scenario is assessed with respect to environmental impact, such as enhanced water quality and potential alterations in phytoplankton communities. Furthermore, we establish integrated nutrient criteria for eutrophication control, concentrating on the management of both N and P inputs while maintaining the current ratio between them. The model results indicate that a 20% reduction in both N and P from European Union (EU) rivers would result in about a 24% decrease in N within the BG and RO 2 nm coastal waters, whilst sustaining the N:P ratio across various spatial scales—from river inputs to coastal and offshore zones. This approach is valuable for assessing the potential impacts of different nutrient reduction strategies, aiding the effective management of marine ecosystems to address eutrophication challenges. Full article

Chlorophyll-a concentration (Chl-a) is a key indicator of marine water quality, phytoplankton biomass, and aquatic ecosystem status. Multi-step forecasting is challenging because Chl-a dynamics exhibit regional heterogeneity, multi-scale variability, and complex spatial dependence. Existing models often optimize domain-averaged errors, which can mask unstable node-level predictions at high-variability nodes. We propose MS-STMoE, a heterogeneity-aware multi-scale spatio-temporal mixture-of-experts framework. It uses a Haversine-distance-based K-nearest-neighbor graph, gated multi-scale temporal convolutions with seasonal encoding to model short-term and periodic variations, and node-level sparse top-k routing that assigns differentiated expert pathways to nodes with distinct dynamics based on recent-state, temporal-mean, temporal-change, and node-prior features. Using 30-day histories to forecast the next 15 days, experiments on 300 Bohai Sea and 265 South China Sea nodes show that MS-STMoE achieves the lowest average MAE and RMSE among six recent spatio-temporal baselines. Compared with the best baseline, MAE and RMSE decrease by 5.6% and 2.7%, respectively, in the Bohai Sea, and by 11.0% and 5.0%, respectively, in the South China Sea. Step-wise and node-wise analyses indicate improved medium-to-late-horizon accuracy and modest, region-dependent reductions in high-error node tails, supporting more reliable region-aware short- to medium-term water quality monitoring. Full article

Accidental releases of radionuclides from nuclear-powered vessels or ships carrying nuclear weapons may expose marine organisms to radioactive contaminants. The consequences of such events can differ markedly between resident fish populations and migratory species that move through affected areas. While these contrasting responses have been evaluated by the authors for coastal nuclear accidents, comparable assessments for open-sea scenarios remain limited. We simulated radionuclide releases from vessels in the North Atlantic to evaluate exposure pathways and potential ecological effects on both resident and migratory fish, since several naval bases operating nuclear-powered vessels are located along the eastern North American coastline. Physical transport of radionuclides was modeled using a Lagrangian framework that incorporates advection by ocean currents, three-dimensional turbulent diffusion, radioactive decay, and dynamic sediment–water exchanges. This transport model was coupled to a four-compartment food-web bioaccumulation model representing phytoplankton, zooplankton, non-piscivorous fish, and piscivorous fish. The approach allows evaluation of contaminant uptake in resident fish populations and along the migration routes of highly mobile species. Bluefin tuna (Thunnus thynnus), a key ecological and commercially valuable species, was selected as the migratory case study. Migration paths reconstructed from electronic tagging data were integrated to estimate radionuclide exposure along individual trajectories. This combined modeling framework provides new insight into how open-sea nuclear releases may differentially affect resident fish communities and wide-ranging migratory species in the North Atlantic, with relevance for fish ecology, population risk assessment, and fisheries management. Full article

Long-term chlorophyll-a (Chl-a) phenology and recurrent high-Chl-a conditions provide important evidence for identifying spatially persistent water-quality concerns in coastal bays. However, seasonally normalized screening of high-Chl-a recurrence at the sampling-cell scale remains limited for subtropical multi-bay coastlines, where regional monsoon forcing, hydrodynamic retention, riverine inputs, aquaculture, and coastal development jointly shape phytoplankton variability. Based on Copernicus Marine ocean-colour records from 2003 to 2024, this study developed a reproducible ~4 km sampling-cell framework for seven coastal bays in Fujian, China. Monthly geometric-mean climatologies, phenological metrics, P90-based high-Chl-a exceedance frequencies, monitoring-priority classes, and exploratory machine-learning diagnostics were derived. Bay-scale phenology showed clear divergence: Sansha and Xinghua Bays exhibited winter or year-end Chl-a enhancement, Xiamen Bay peaked in summer, and Quanzhou Bay reached an early-autumn maximum. Four seasonal phenological regimes further revealed cell-scale heterogeneity, with C2 representing winter-enhanced, high-amplitude cycles and C3 identifying cells with the most frequent seasonally normalized high-Chl-a exceedances. High- and moderate-priority cells were concentrated mainly in Sansha and Xinghua Bays, whereas Dongshan and Quanzhou Bays showed only localized priority cells. Exploratory diagnostics indicated that distance to the bay mouth was the most important correlate of recurrent high-Chl-a susceptibility, suggesting the role of bay-scale exchange and retention gradients. This framework converts long-term ocean-colour archives into spatially explicit phenological and anomaly-screening evidence to support targeted coastal water-quality monitoring and ecosystem management. Full article

Small pelagic fishes play a crucial role in structuring marine food webs, yet their trophic flexibility and feeding interactions remain poorly understood in highly dynamic, nutrient-rich systems such as upwelling regions. This study combines bulk stable isotope analysis (δ¹³C and δ¹⁵N), compound-specific nitrogen isotope analysis of amino acids (CSIA-AA), and fatty acid (FA) profiles to assess feeding patterns and trophic overlap among four planktivorous species in the North Iberian shelf (Galicia and the Cantabrian Sea). The combined trophic indicators reveal clear niche partitioning between clupeids (sardine and anchovy) and scombrids (mackerel and chub mackerel), with the latter exhibiting higher CSIA-AA-derived trophic positions and distinct FA composition. Our analysis further shows that fatty acid biomarkers are essential for resolving finer-scale differences within each group, driven by variable contributions of phytoplankton and zooplankton to species diets. Although all species shared resources within the same food web, isotopic baselines indicate a decoupling between carbon and nitrogen pathways. For sardine, we compared neutral and polar lipid fractions with the total lipid extract in terms of FA composition and key dietary markers. Our results suggest that separating lipid fractions can improve dietary resolution, especially when lipid content is low. Overall, our findings highlight the value of integrating classical and emerging biochemical tracers to better resolve trophic dynamics in coexisting planktivorous fishes. Full article

In the Mahanadi Basin (Site U1445), the mean δ¹³C_SOM (i.e., δ¹³C of sedimentary organic matter) value is consistently higher during the glacial periods (–18.8‰) than during the interglacial periods (–19.4‰), which implies either more deposition of terrestrial organic matter from C4 plants or increased marine primary production (MPP). We attempted to quantify the relative contributions of organic matter by C3 plant, C4 plant, and MPP, using the three end-member simple mixing model (IsoSource). This study reports that their partitions are distinctly different between the interglacial (29%, 28%, and 43%) and glacial (22%, 40%, and 38%) periods, despite the model’s limitations. The contribution of allochthonous terrestrial organic matter overwhelms the production of autochthonous marine organic matter in the Mahanadi Basin, particularly during the glacial periods, emphasizing that the freshwater discharge by the Indian monsoon precipitation is a key process of the organic carbon cycle. Our results also verify that C4 plants were more distributed in the Himalaya foreland during the glacial periods under the decreased atmospheric pCO₂ and humidity levels. Different contribution of terrestrial organic matter sources to the Mahanadi Basin depends on the orbital-scale Indian monsoon variability, highlighting the land–sea transfer of organic carbon. Full article

Multiple environmental stressors can directly or indirectly affect zooplankton community structure in marine coastal waters. However, quantifying the relative importance of eutrophication-mediated pathways remains challenging. In this study, we surveyed zooplankton, phytoplankton, and water conditions at 24 stations in Qinzhou Bay during spring and used correlation analysis and structural equation modelling (SEM) to examine the association between eutrophication and zooplankton biomass. The results showed that zooplankton biomass increased from the Inner Bay to the Outer Bay; whereas, zooplankton evenness decreased. Biomass was significantly negatively correlated with both the eutrophication index and zooplankton evenness; a single small copepod numerically dominated the assemblage, so high biomass and low evenness co-occurred as expressions of dominance. The SEM showed an acceptable fit and linked eutrophication to lower zooplankton biomass mainly through heavy-metal enrichment, community dominance (low evenness), and reduced phytoplankton density. The total association between eutrophication and biomass was −0.40, primarily indirect rather than through a significant direct path (−0.13, p = 0.51), with heavy-metal enrichment and community dominance (low evenness) as the main statistical mediators. Because the data come from a single spring survey of 24 stations, these path coefficients should be interpreted as correlational associations requiring multi-season confirmation. Full article

Marine chlorophyll-a (Chl-a) concentration is a key proxy for phytoplankton biomass and an important indicator for eutrophication assessment, ecological monitoring, and harmful algal bloom early warning. Accurate forecasting of Chl-a concentration therefore has substantial scientific and practical value for marine environmental management. Nevertheless, existing deep models still have difficulty coupling relatively stable large-scale spatial structure with locally time-varying interactions, and many of them do not provide reliable uncertainty estimates, which limits their use in harmful algal bloom early warning and high-chlorophyll event assessment. To address these issues, this study proposes an uncertainty-quantified dynamic graph ordinary differential equation network, termed UQDGODE, for marine Chl-a concentration forecasting. The model combines a multivariate diffusion graph convolutional branch for stable spatial diffusion modeling with a dynamic graph ordinary differential equation branch for continuously evolving local interactions. A gating mechanism fuses the two branches, and a multivariate probabilistic prediction module outputs predictive means and covariance information for uncertainty quantification. Experiments on the Bohai Sea and South China Sea datasets show that the UQDGODE performs better in both point forecasting accuracy and probabilistic forecasting quality and produces more informative predictive distributions and more adaptive prediction intervals for marine ecological alerting. Full article

Monitoring phytoplankton diversity is essential for the conservation of marine ecosystems and the protection of human health. This study compares light microscopy (LM) and DNA metabarcoding (MB) for analysing phytoplankton community at a long-term station in the Central Adriatic Sea, representing the first application of metabarcoding in this region. Sampling was conducted in June 2024 using Niskin bottles and a 53 µm plankton net. Four genetic markers (COI, 18S V4, 18S V9, rbcL) were applied to bulk plankton DNA to broaden taxonomic coverage and assess their detection performance relative to LM. Among the molecular markers, rbcL detected the highest taxonomic richness and was particularly effective for diatom species detection. In contrast, 18S V4 and 18S V9 captured a broader spectrum of phytoplankton diversity, especially outperforming LM and the other two molecular markers in detecting a previously unrecognized but ecologically important phytoflagellate group. Species-level resolution within the taxonomically challenging genera Chaetoceros and Pseudo-nitzschia was considerably improved with metabarcoding. However, several taxa observed by LM, including certain coccolithophores and thecate dinoflagellates, were not detected by any of the molecular markers. Overall, the results show that methodological choices strongly influence biodiversity estimates and highlight the value of a complementary integrative approach in assessing phytoplankton diversity. Full article

Phytoplankton are the major primary producers in the Southern Ocean, are important to global nutrient cycles, and are at the base of marine food webs. Polar ecosystems are unique in their extended periods of darkness in the winter, and prolonged darkness has the potential to exert selection that affects diatom population composition if there is differential survival in the dark, the variation in population growth rates in subsequent light periods, or both. We tested whether prolonged darkness has the potential to exert within-species selection on a model polar diatom species by exposing five strains of the polar diatom Porosira glacialis to prolonged darkness at two different temperatures in the laboratory. We measured population survival in the dark, growth rate upon re-illumination, and between-strain variability in these traits. We found a pronounced decline in survival and growth rate with time spent in the dark, as well as important intraspecific variation in the tested strains. Declines in survival and growth were exacerbated at a higher temperature. Our results show that the darkness of polar night can exert intraspecific selection in a common Southern Ocean diatom. Full article

Coastal water quality in the Bothnian Sea is shaped by interactions among local nutrient inputs, internal nutrient cycling, and basin-scale phosphorus enrichment, complicating the assessment and management of eutrophication. This study analyses long-term time series of nutrients (total phosphorus (TP), dissolved inorganic phosphorus (DIP), dissolved inorganic nitrogen (DIN), and total nitrogen (TN)) and phytoplankton indicators (chlorophyll a and biomass) from contrasting Finnish coastal systems off Uusikaupunki and Rauma. Despite higher external phosphorus loading in Rauma, nutrient concentrations and phytoplankton biomass remain lower than in the semi-enclosed Uusikaupunki coastal zone. In contrast, Uusikaupunki exhibits higher chlorophyll a concentrations and lower TP:Chl a ratios, suggesting greater phosphorus bioavailability. At the offshore station SR5, TP and DIP increase below the surface layer, while surface concentrations show no significant trends, indicating phosphorus accumulation in deeper waters. Declining DIN:DIP ratios indicate a shift toward nitrogen limitation, under which primary production increasingly depends on phosphorus-supported nitrogen fixation. Chlorophyll a increases across the coastal gradient, including the outer archipelago, indicating a spatial expansion of eutrophication. Together, these findings are consistent with a system-level shift toward phosphorus-driven production. The results demonstrate a dual-control system in which basin-scale phosphorus enrichment determines long-term background conditions, while local nutrient loading and legacy effects regulate spatial variability in ecosystem response. More broadly, the findings highlight the importance of cross-scale interactions between regional nutrient enrichment and local ecosystem processes for understanding and managing eutrophication in inland and semi-enclosed marine systems. Full article

Climate-driven changes in oceanographic conditions are increasingly affecting the distribution of marine species, particularly vulnerable elasmobranchs. The undulate ray, Raja undulata, is a Near Threatened batoid species distributed throughout the northeastern Atlantic Ocean and parts of the Mediterranean Sea, yet its potential response to future climate change remains poorly understood. This study assessed current and future habitat suitability using species distribution modelling approaches and CMIP6 climate projections under the SSP245 scenario. Species occurrence records were compiled from biodiversity databases and published sources, and environmental predictors were selected following multicollinearity screening. Among twelve evaluated modelling algorithms, MaxEnt showed the highest predictive performance (AUC = 0.99; TSS = 0.95) and was selected for subsequent analyses. Current habitat suitability was concentrated along the Iberian Peninsula, the Bay of Biscay, the English Channel, and parts of the western Mediterranean Sea. Future projections indicated substantial habitat contraction, with habitat loss (57.3%) greatly exceeding habitat gain (2.2%), resulting in a southward redistribution of suitable habitats. Minimum phytoplankton concentration, sea surface temperature, and silicate concentration were identified as the most influential environmental predictors. Areas predicted to remain suitable under both current and future conditions may represent important climate refugia for the species. Overall, the results indicate that R. undulata is highly vulnerable to future environmental change and highlight the need to incorporate climate-driven habitat shifts into conservation planning, fisheries management, and long-term monitoring strategies. Full article

Phytoplankton are primary producers in the aquatic ecosystems whose pigments, cell size, and physiological state affect how they absorb light and fix carbon. The phytoplankton absorption coefficient (ɑ_ph(λ)) in the visible spectrum is a fundamental cellular optical property that determines phytoplankton–light interactions in the marine environment. This property links biological processes to ocean color remote sensing reflectance (Rrs), enabling an assessment of environmental and biogeochemical conditions in the ocean using ocean color satellites. This study presents a multi-stage systematic review of six decades (1965–2025) of ɑ_ph(λ) research, with a focused synthesis of developments in the past decade. A bibliometric analysis empirically examines the research growth of the field and its thematic convergence into methodological divergence across six decades. Cluster analysis was used to compile influential research topics as well as emerging trends, to determine the scope and design of the systematic review. A focused systematic review of studies in the past decade (2015–2025) has been carried out to identify conceptual and theoretical advances, major observational and algorithmic improvements, and ongoing challenges. The data analyses highlight the accuracy achieved by various studies, the complexity of applications of algorithms, and product-focused developments. The ongoing challenges identified include resolving optical degeneracy, vertical structure acquisition, and scaling methods for operational use. This review concludes the centrality of ɑ_ph(λ) as a key parameter to next-generation ocean color science, biogeochemical modeling, and climate-related ecosystem monitoring. Full article

The Jabal Ali Marine Sanctuary, Dubai, is one of the most important marine protected areas (MPAs) in the UAE. The Arabian Gulf is characterised by extreme environmental conditions, including high temperatures and hypersaline waters. These conditions, combined with increasing anthropogenic pressures from coastal development projects such as desalination plants, energy plants and the Palm Jebel Ali development, may influence the pelagic ecosystems of MPAs. This study examined seasonal variability in phytoplankton communities and environmental conditions between summer (June 2017) and winter (December 2017), with particular emphasis on the interactions between temperature-driven stratification, hypersaline conditions, and phytoplankton community structure, abundance, and diversity. The AZTI (AZTI Tecnalia Marine Research Centre) Marine Biotic Index indicated predominantly “Good” to “High” ecological status of the pelagic ecosystem, indicating favourable environmental conditions. Potentially harmful algal bloom taxa, including Pseudo-nitzschia and Dinophysis, were detected at low abundances. Summer surveys recorded higher total species richness (44 vs. 34 species) and greater phytoplankton abundance (mean 68.6 vs. 49.8 cells/L) compared to those in winter. Diatoms dominated the assemblages in both seasons, accounting for 62–69% of the recorded species, while distinct spatial zonation patterns reflected habitat heterogeneity. The observed seasonal and spatial variability highlight the importance of incorporating temporal and spatial dimensions into management strategies. As the first pelagic phytoplankton assessment conducted in an MPA, this study provides important baseline data for understanding phytoplankton ecology in one of the world’s most environmentally extreme marine ecosystems. The findings contribute to evidence-based management under increasing climate change and anthropogenic pressures. However, because sampling was limited to the two principal climatic seasons, the study characterises inter-seasonal variability rather than a complete annual succession cycle. Additional surveys during spring and autumn are recommended to fully resolve seasonal succession dynamics. Overall, the findings support the continued protection of the sanctuary as an important biodiversity reservoir and a potential reference site for assessing marine ecosystem responses to environmental conditions. These findings are directly relevant to the environmental sustainability agenda of the Dubai 2040 Urban Master Plan, which prioritises the protection and expansion of the emirate’s nature reserves and the safeguarding of marine and coastal biodiversity. By establishing the first pelagic phytoplankton baseline for the sanctuary, this study provides an evidence base for monitoring and managing marine protected areas in line with this long-term framework. Full article

Domoic acid (DA) is a well-known seafood toxin produced by some species of marine phytoplankton in the genus Pseudo-nitzschia during harmful algal blooms (HABs). Acute toxic exposures induce overt clinical signs of neuroexcitotoxicity, such as seizures in mammals due to overstimulation of glutamate receptors in the central nervous system (CNS). Acute DA excitotoxicity via the CNS has been well-studied in both field poisoning events and laboratory exposure studies with rodent models, but little is known about the impacts of low-level DA exposures below those that cause outward signs of neurotoxicity; the impacts on other potential target organs, including the heart; or age-related sensitivities. Here, low-level DA exposures in young adult (9 mo) and old (24 mo) mice were conducted over multiple weeks. Mortality, cardiac function, frailty, and protein expression were quantified to assess age-related DA sensitivity and potential impacts on heart function. Echocardiography and proteome data confirm that chronic low-level DA exposure causes irreversible functional cardiomyopathy and protein remodeling in young adult mice that mimics natural cardiac aging. In addition, old mice exhibit higher mortality and frailty than young adult mice with the same low-level DA exposures. These results provide critical information for assessing potential health risks to humans who regularly consume seafood with low levels of DA. Full article